The invention relates to a magneto-optical waveguide having a magneto-optical layer applied on a substrate layer.
Such a waveguide is disclosed in the GB-A 1,529,374. More specifically when these waveguides are used for optical insulators and circulators, the problem is the matching of the propagation constants .beta..sub.TE and .beta..sub.TM of the TE-modes, or TM-modes, respectively, which can be fed into the waveguide. Its difference .DELTA..beta. must have an accurately predetermined value to provide an adequate insulation. For the majority of applications .DELTA..beta. must be equal to 0.
A desired value .DELTA..beta. cannot be obtained with a sufficient accuracy when a magneto-optical layer is grown epitaxially. Layer deviations of less than 0.1 .mu.m, which are caused by the tolerances, result already in unacceptable changes in the value of .DELTA..beta.. Consequently correction measures are necessary to accomplish a phase match. In the prior art a metal layer provided at some distance from the magneto-optical layer is used for that purpose. The accurately required setting of the distance causes difficulties.
As is disclosed in Opto Electr. Magazine 87, pp. 238-246, an anisotropic covering layer, consisting of vacuum-deposited strips in a grid pattern can be used for the face match. The production of this known covering layer is expensive. The strip period and the strip width can indeed theoretically be chosen such that, for example, a value .DELTA..beta.=0 is the result. In practice this ideal state aimed at cannot be obtained with a sufficient degree of certainty and accuracy. On the one hand a theoretic predetermination of the strip width and the strip period is comparatively uncertain and on the other hand the data obtained can significantly deviate because of unavoidable manufacturing tolerances of the desired value.
A method described in Proc. ECOC, Barcelona, 186, in which the setting of .DELTA..beta. is possible by means of specific mechanical stresses applied from the exterior, requires expensive and bulky additional devices.